Both for vehicle seat height adjusters and also for backrest adjusters, so-called lever drives are known for operating or adjusting the seat function. Such lever drives are bi-directional step switching mechanisms, the actuating angle of which is generally 15 to 30°, and which only transmit the respective actuating direction and are decoupled from the drive output on the return path. Such mechanisms are conventional as load-absorbing systems in height adjusters. In the application as a backrest adjuster, generally the driven backrest fitting, which is designed as a geared fitting, absorbs the usage and crash loads. Known drive devices are disclosed in DE 103 55 821 B4, DE 103 40 997 B3, DE 100 52 089 C1 and DE 100 19 854 C2.
In particular during the actuating of a geared fitting as a backrest adjuster, the idle stroke which is provided and necessary in the geared fitting for the purpose of controlling various components (switching spring, wedges, etc.) is a hindrance in combination with lever drives, because the operating lever travel is often only 15°, while the idle travel of the backrest adjuster is however of a similar order of magnitude. To overcome these circumstances, use has therefore often been made, as one function, of a step-up gearing which expediently interacts directly with the operating lever. The further function of a step switching mechanism is implemented in the abovementioned solutions as a positively locking clutch which is situated spatially behind the gearing and which has toothed bolts and an internal gear toothing. If used for a geared fitting of a backrest adjuster, a further function, a maximum load limitation, is expedient, because such geared fittings are optimized for direct operation by means of a hand-operated wheel, and the maximum structurally admissible torques which can be introduced directly by hand are considerably lower than the torques introduced by means of levers. As a result of these three functions, and the conventionally structurally very different implementation of the respective individual functions in the form of components, the abovementioned overall solutions are in effect constructed as individual functional assemblies connected one behind the other in series. This ultimately results in a multiplicity of individual components, corresponding production costs and a considerable installation space requirement.